Permeability studies of water through the skin and flesh of d'Agen plums have been carried out by radiotracer and PGSE NMR techniques as a function of moisture content. The results have shown that the diffusion coefficient of water through the skin layer increases as the fruit is dried at 70 degrees C or above. By contrast, the water diffusion through the fruit becomes more hindered as moisture is lost and structural collapse of the cell layers takes place. Values for diffusion coefficients of water at 21 degrees C through the fruit of 1 x 10(-9) m(2) s(-1) for fresh plums and 2.0 x 10(-10) m(2) s(-1) for fruit dried to 50% moisture content (wet basis) were found. Structural studies using scanning electron microscopy techniques were also performed. These showed that drying induces marked changes to the waxy skin layer of the fruit as well as the fruit flesh. These results are discussed in terms of the important role that the plum skin has in modulating the moisture loss process during dehydration, particularly at early stages of drying.

p–V–T data for six compositions of 2-n-butoxyethanol (BE) and water have been obtained in the form of volume ratios at several temperatures in the range 278.15 to 353.13 K at pressures from atmospheric to 347 MPa or higher. One of the compositions is in the region where two phases exist at certain temperatures, while two compositions are near the boundary of that region. Densities at atmospheric pressure in a temperature range similar to that for the p–V–T data are also reported. Isothermal compressibilities, isobaric expansivities, and changes in the isobaric heat capacity have been calculated from the volumetric data for pressures up to 300 MPa. The values of normalized volume fluctuations obtained from the data at 0.1 MPa approach those of water for conditions which are close to those for phase separation in this system. Such behavior is not observed at 100 MPa, where such separation is suppressed.

The effect of pressure on the volume of aqueous solutions of 2-methyl-2-propanol (t-butyl alcohol) has been measured as the ratio of the volume under pressure to its value at 0.1 MPa with a bellows volumometer for temperatures from 5 to 75 degrees C at pressures up to 300 MPa. Six compositions have been used covering the mole fraction range from 0.025 to 0.45 as well as pure 2-methyl-2-propanol. Isothermal compressibilities and thermal expansivities have been calculated from the results. Significant features in those properties are discussed. The data have also been fitted to Hayward and Tait equations of state.

The effect of pressure on the volume of tetrahydrofuran (THF) has been measured as the ratio of the volume under pressure to its value at 0.1 MPa pressure with a bellows volumometer for temperatures fromT=(278 to 323) K at pressures up to 300 MPa. Similar measurements have been made for two of its mixtures with water,x(THF)=(0.25 and 0.5) for temperatures fromT=(288 to 338) K. The data have been fitted with two equations of state. Densities at atmospheric pressure have been measured for THF and for aqueous mixtures of THF. For the latter the densities cover the composition range (0.2≤x≤0.8) at the temperatures (288, 298, and 313) K and smaller ranges of composition at higher temperatures. Isothermal compressibilities, volume fluctuations, thermal expansivities, and the change in isobaric heat capacity from its value at 0.1 MPa pressure have been calculated. Significant features on these properties are discussed.

A two-stage model has been used successfully to predict the drying curves for d'Agen prunes. The model assumes the drying process occurs in two distinct stages. First, a period where the evaporation of water from the surface of the drying fruit is the limiting factor for the moisture loss is assumed. This results in a constant rate of water loss. A second period of drying occurs when a water concentration gradient has been established within the plum. During this time, the rate of moisture loss is limited by the mass transfer of water through the fruit, leading to a falling rate of evaporation of water at the fruit surface. This model predicts reasonable values for the moisture loss as a function of drying time. Significant discrepancies between the experimental results and the model occur only for a longer drying time at the higher temperature range (e.g. 90 degrees C and above). This is due mainly to uncertainty in the value for the equilibrium moisture loss caused by other weight loss processes in the latter stages of drying such as thermal degradation of carbohydrates. (C) 1997 Elsevier Science Ltd.

The effect of pressure on the volume in the liquid phase for chlorobenzene and 1,2-dichlorobenzene has been measured relative to their volumes at 0.1 MPa with a bellows volumometer for pressures up to 300 MPa over the temperature range (278.15 to 338.13) K. The experimental volume ratios have been represented by two sets of equations to enable interpolation and extrapolation of volumetric properties. The results of one of these representations suggests a means of extrapolating the volumetric properties of these chloro-substituted benzene derivatives. Isothermal compressibilities, thermal expansivities, normalized volume fluctuations, and the change in the isobaric heat capacity from its value at 0.1 MPa have been calculated from the results.

The use of imaging schemes which employ large pulsed magnetic-field gradients to avoid susceptibility and diffusion artifacts in NMR microscopy is considered. The theory relating to these artifacts is briefly reviewed in the context of two specific pulse sequences, namely two-dimensional (i.e., slice-selective) phase-phase encoding and two-dimensional phase-frequency encoding in which the magnetization is recycled in a CPMG multi-pulse train. Experiments have been carried out using a specially constructed coil set which achieves gradient strengths of up to 6 T m(-1) and a number of images are shown, both from a susceptibility phantom and from a geranium petiole. Some of the inherent advantages and disadvantages of the respective imaging schemes are demonstrated.

Terbium ethyl suphate (TbES) has been studied by nuclear orientation using radioactive Tb-160. It is found that (i) it is difficult to cool the terbium nuclei below approximate to 50 mK because of the long nuclear spin-lattice relaxation time T-1N; (ii) application of small magnetic fields of the order 0.1T produces a dramatic increase in the value of T-1N; (iii) the long electronic relaxation time T-1E makes it difficult to determine the Curie temperature Te in such experiments; and (iv) the saturation magnetic moment is approximately 7.35 mu B. No nuclear magnetic resonance transitions were detected when radio-frequency fields at frequencies from 190 to 920 MHz were applied, but a long series of resonance absorption peaks was observed with a frequency separation of 26.3(3) MHz. Their origin is ascribed to magneto-acoustic modes within magnetic domains, rather than to magnetostatic modes, magnetic spin waves, or resonances within domain walls.

Recently, pulsed NMRON experiments have been carried out on trace amounts of radioactive54Mn in the antiferromagnet MnCl24H2O at 500 MHz (Le Gros et al. [1]). In this compound, the quadrupole splitting between the two lowest NMR transitions is ≈3 MHz, which precludes the use of non-selective (hard) rf pulses. Yet within the restricted 2*2 manifold, associated with a given transition, the nuclear rotation is “hard”. In this paper, the theory of “selective-hard” NMRON and MQ-NMR experiments is developed within the framework of irreducible tensor operators. In essence, the theory extends the early work of Jaynes [4] to deal with the higher-order multipolar states created during the course of a given NMR experiment. Several new pulsed NMRON and MQ-NMR experiments are proposed. For example, it is demonstrated how “ouble resonance”, “selective-hard” experiments on the pseudo spin-1 manifold spanned by |±1> and |0> Zeeman states of any integer spinI could be used to extract small chemical shifts in the face of very large quadrupole splittings.

The principal advantage of the n.m.r. imaging method lies in the specific contrasts which are available. In this work we describe the use of velocity and diffusion contrast methods in biophysical applications and at microscopic spatial resolution. In the first example, involving water-protein interactions, the relationship between water self-diffusion and water concentration, as measured using pulsed gradient spin echo n.m.r., is shown. It is demonstrated that this relationship can be used to provide a water concentration image. The result is compared with the conventional proton density and transverse relaxation maps. The next example concerns the use of dynamic n.m.r. microscopy to obtain water diffusion and velocity maps for wheat grain in vivo. Finally we suggest how the method may be used in the study of polymer-water interactions in an unusual adjunct to conventionalf polymer self-diffusion studies.

Nuclear orientation and nuclear magnetic resonance measurements have been performed for {sup 106}Rh oriented at low temperature in iron and nickel hosts. From the results of the temperature dependence measurements of nuclear orientation, the magnetic moment of {sup 106}Rh was deduced as {vert bar}{mu}({sup 106}Rh,1{sup +}){vert bar}=2.52(5){mu}{sub {ital N}}, which is very different from the value of 3.07(9) {mu}{sub {ital N}} reported previously. From the nuclear magnetic resonance on oriented nuclei measurements of {sup 106}Rh{ital Ni}, the magnetic hyperfine splitting frequency {vert bar}{ital g}{mu}{sub {ital N}}B{sub HF}/h{vert bar} was determined to be 441.5(7) MHz. Using the hyperfine field {ital B}{sub HF} (Rh{ital Ni}) of {minus}22.49(5) T, the precise value of the magnetic moment of {sup 106}Rh was deduced: {vert bar}{mu}({sup 106}Rh,1{sup +}){vert bar} =2.575(7) {mu}{sub {ital N}}. The electric quadrupole interaction has been measured using modulated adiabatic passage on oriented nuclei in a nickel single-crystal host. A broad distribution of the quadrupole splitting {Delta}{nu}{sub {ital Q}} is found, extending from 0 to 300 kHz.

Nuclear spin-spin relaxation of60Co and56Co in iron single crystals has been studied, using the three-pulse NMRON spin echo. A previously reported rapidT2 in60CoFe is shown to have arisen from a modulation of the echo amplitude, caused by variations in the phase of the Larmor precession relative to the applied rf field. A lower limit ofT2∼0.2s is found in56Co56Fe. Extension of this result to other CoFe samples is discussed.

The analysis of spin-lattice relaxation (SLR) of very dilute impurity nuclei in ferromagnetic hosts, as encountered in NMR of oriented nuclei (NMRON), usually neglects the spin-spin interaction, assuming a no-spin-temperature model. However, the regime of impurity systems for which this assumption is valid has not been established. the relaxation following single passage in60CoFe<110> and55CoFe<100> has been measured, and is compared with calculations made with and without a spin-temperature constraint.

The electric quadrupole interactions at57Co and60Co in co-diffused57,60CoFe single crystal have been measured using Modulated Adiabatic Passage on Oriented Nuclei (MAPON). The quadrupole splittings ΔνQ<100> are + 18(2) kHz for57Co and +9(2) kHz for60Co, corresponding to a principal electric field gradient (efg) tensorV zz =2.0(5)×1019 Vm−2 and 2.5(6)×1019 Vm−2, respectively, in broad agreement with previous MAPON results for CoFe. The distributions of the efg’s are very similar for the two isotopes, verifying that previously reported differences in58CoFe and60CoFe could be attributed to different host preparations. The measurement of such weak efg’s which are not spectroscopically resolved, allows determination of new nuclear electric quadrupole moments, not accessible by other techniques. Applications to other systems are discussed.

The new technique of modulated adiabatic passage on oriented nuclei (MAPON) is shown to provide self-consistent signs and magnitudes for the principal component of the electric-field-gradient tensor at $^{60}\mathrm{Co}$ and $^{58}\mathrm{Co}$ nuclei in single-crystal iron. The best result for the mode value is ${V}_{\mathrm{ZZ}}$=+3.4(5)\ifmmode\times\else\texttimes\fi{}${10}^{19}$ V/${\mathrm{m}}^{2}$. A further test of MAPON using $^{56}\mathrm{Co}$ in single-crystal iron yields a quadrupole moment of ${Q}_{56}$=+25(9) ${\mathrm{fm}}^{2}$, in excellent agreement with systematics and theory. Experimentally derived distributions in electric field gradients are found to be consistent with sample-preparation procedures. These results firmly establish MAPON as capable of resolving extremely fine features in the electronic charge distribution at nuclear probes and with the wide applicability and sensitivity of nuclear-magnetic-resonance spectroscopy on oriented nuclei.

The anisotropic \ensuremath{\gamma}-ray distribution from oriented nuclei (ON) may be used to detect changes in the ensemble spin polarization and, in particular, those changes arising from nuclear magnetic resonance (NMR ON). A feature of NMR ON of dilute nuclear impurities in ferromagnets is the severe inhomogeneous broadening resulting from a distribution of magnetic hyperfine fields over the nuclear ensemble. In conventional NMR ON spectroscopy fine details of the hyperfine interaction, such as the electric quadrupole interaction, are buried in the inhomogeneous broadening. It is shown here that the quadrupole splitting may, however, be directly measured if the rf field is amplitude modulated during an adiabatic passage. Such a modulation implies a three-level coupling which is sensitive to rank-2 terms in the hyperfine Hamiltonian, and the modulation frequency corresponds to the spectral domain of the quadrupole splitting. This theory is developed and applied to nuclear ensembles with integral and half-integral spins.

Typical linewidths observed in NMRON on dilute impurities in ferromagnetic metals are of order 1 MHz, making difficult the observation of structure in the resonance with splitting Δv much less than this value. The technique of Modulated Adiabatic Passage on Oriented Nuclei (MAPON) was recently developed as a means of measuring the weak electric quadrupole splitting ΔvQ of the nuclear hyperfine interaction due to an electric field gradient Vzz. MAPON has successfully been applied to measure ΔvQ as low as 4 kHz, i.e. less than 0.5% of the inhomogeneously broadened NMRON CWFM resonance line. The isotopes56Co,57Co,58Co and60Co have been studied in iron single crystal hosts, yielding ΔvQ consistent with known and estimated quadrupole moments. In addition the results to date give striking confirmation of analyses based on the single impurity relaxation model. Following a brief summary of the theoretical development of MAPON a review of experimental data is given for the CoFe<100> system. The variation of ΔvQ with direction of magnetization, measured in58CoFe and60CoFe single crystal samples, is also described. Further MAPON measurements are described for a56CoFe polycrystalline sample, for which the most probable value and width of the distribution of Vzz can be described simply in terms of the single crystal principal axis results. The application of the MAPON technique to the measurement of nuclear electric quadrupole moments in implanted and diffused samples is discussed.

Adiabatic Fast Passage NMR/ON measurements on single crystal56CoFe indicate a unique electric field gradient when the applied field is parallel to the 〈100〉 direction.

A novel extension of the Single or Adiabatic Fast Passage NMR/ON technique is described. Its principal advantages in extracting the mode magnitudes and distribution widths of weak nuclear electric quadrupole splittings much less than the magnetic inhomogeneous broadening are its simplicity and generality requiring no assumptions on the degree of adiabaticity of the nuclear spin motion during sweep through the quadrupolar split subresonances. The technique is applied to a concentrated single crystal sample of60CoFe which failed to yield a well resolved mid passage signal to conventional single passage NMR/ON. The result is an asymmetric frequency distribution of quadrupole frequencies with a mode value of P=3e2qQ/4I (2I-1)=+4.5 ±1.0 kHz and half maxima of +2.5 kHz and +7.0 kHz.